Electrochromic display device

ABSTRACT

A chemically coupled color-changing matrix display device is disclosed wherein the display material is a surfactant-treated color changing metal-diphthalocyanine complex. For example, lutetium diphthalocyanine may be treated with a mixture of silicone glycol and imidazoline surfactants to provide a deposit having substantially the same color as electrolytically cycled deposits of the same material. 
     Also disclosed is a non-electronic chemical sensing device comprising a surfactant-treated electrochromic metal diphthalocyanine complex. Upon exposure to a hazardous gas such as chlorine, the surfactant-treated material undergoes a change in color.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

This invention relates to electrochromic devices. In one aspect itrelates to electrically controllable display devices. In another aspectit relates to electrically tunable optical or light filters. In yetanother aspect it relates to a chemical sensor device which employs acolor changing film.

There are many uses for electrically controllable display devices. Anumber of such devices have been in commercial use for some time. Thesedisplay devices include liquid crystal displays, light emitting diodedisplays, plasma displays, and the like. Light emitting diode and plasmadisplay panels both suffer from the fact that they are active, lightemissive devices which require substantial power for their operation. Inaddition, it is difficult to fabricate light emitting diode displays ina manner which renders them easily distinguishable under bright ambientillumination. Liquid crystal displays suffer from the disadvantage thatthey are operative only over a limited temperature range and havesubstantially no memory within the liquid crystal material. Further, thevisibility of many liquid crystal displays decreases as the viewer movesa few degrees off axis.

Electrochromic displays have been developed which display informationthrough a change in color of portions in the display. In certain ofthese displays the color change is accomplished by way of reversibleelectro-precipitation of certain cations onto a transparent electrode.In certain other of these displays a metal ion in the electrolyte isreversibly reacted with a transparent electrode. In these knownelectrochromic displays, coloration is induced employing an externalpotential. By reversing the original potential, or by applying a newpotential, it is possible to cancel, erase or bleach the visiblecoloration. These steps of color induction and erasure are defined ascycling.

Because of their operative mechanisms, the known electrochromic displaydevices have suffered the drawbacks of requiring substantial powerand/or time to write or erase displayed information.

Rare earth diphthalocyanines are known to have electrochromic propertiesin which the color of the diphthalocyanine can change over a period ofabout 8 seconds upon application of a potential difference across anelectrochemical cell having a diphthalocyanine film on one of theelectrodes. The diphthalocyanine does not require large amounts of powerto change color, but the long period required for the color to changemakes known diphthalocyanine performance characteristics unacceptablewhen measured against display requirements.

Nicholson, U.S. Pat. No. 4,184,751 describes electrochromic displaydevices using a metal diphthalocyanine complex as the electrochromicmaterial in which displayed information can be switched in 200milliseconds or less by constructing the device so that the apparent RCtime constant of the overall structure is one second or less. Amulti-color, i.e., more than two color, display is achieved through useof a range of voltages applied between display and counter electrodes.Color reversal of displayed information and the background against whichit is displayed is achieved through use of display electrodes in thebackground portions of the viewing area as well as in the charactersegments.

In a simpler tYpe of displaY device where color reversal is not requiredthe background portions of the viewing area are often provided withdeposits of the display material surrounding and conforming to theoutlines of the segmented character electrodes. This feature is intendedto provide a uniform appearance to obscure the character electrodes whenthe display device is in the erase condition.

In such a device, the metal diphthalocyanine display material has aninitial color in both the background regions and on the character ordisplay electrodes. Upon electrical cycling, however, the displaymaterial on the display electrodes typically does not return to theprecise initial color. This is objectionable in a display device.

Several approaches have been proposed for use in solving the problem ofthe failure of the erased display electrodes to match the color of thebackground. Most such proposals are relatively expensive either in termsof materials or processing steps. Nicholson et al., in U.S. patentapplication Ser. No. 330,041, filed Dec. 11, 1981, now abandoned,disclose a simple, inexpensive method for treating an electrochromicdisplay material in order that the background and cycled materials havesubstantially the same color. The method comprises treating a depositeddisplay material with a liquid vehicle containing substitutedimidazoline and silicone glycol surfactants, then driving the liquidvehicle from the deposited display material. Where the display materialis lutetium diphthalocyanine, the resulting color is olive-green. In thewritten state, the color is bright green; in the erased state the coloris olive-green.

Matrix display devices contain one or more arrays of many small elementsor dots of color changing material that can be selectively activated orswitched to form virtually any alphanumeric or graphic pattern. Tocreate such patterns and erase them at will some means must be providedto access each element independently without activating those in thesurrounding area. It has been proposed to build an integrated drivematrix of thin-film transistors into a display device so that eachelement is provided, in effect, with a separate switch connecting it tothe power supply. A simpler approach is to use a multiplexed addressingscheme. Nicholson U.S. patent application Ser. No. 327,856, filed Dec.7, 1981, now U.S. Pat. No. 4,456,337, describes a chemically coupleddisplay device which may be addressed by direct multiplexing of two setsof parallel conductive, linearly-extending electrodes disposed at rightangles.

Electrically tunable filters consist of a film of color-changing filtermaterial wherein the color of the filter is electrically tunable.Nicholson, U.S. patent application Ser. No. 451,294 filed Dec. 20, 1982,now U.S. Pat. No. 4,501,472 describes an electronically tunable filterand an electronically switchable light valve which is capable of beingreversibly changed from light transmissive in one state to opaque inanother.

It is an object of the present invention to provide an improvedchemically coupled color-changing display device.

It is another object of this invention to provide an improved tunableelectrochromic filter.

It is yet another object of this inventlon to provide an improvednon-electronic chemical sensing device.

Other objects, aspects, and advantages of the present invention will beapparent to those skilled in the art.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention there isprovided a low power, rapid switching, electrochromic device comprisinga surfactant-treated electrochromic metal diphthalocyanine complexdisplay matrix and an electrolyte which comprises at least one chemicalcolor switching agent.

In accordance with another embodiment of the present invention there isprovided an electronically tunable color filter comprising asurfactant-treated electrochromic metal diphthalocyanine complex filtermaterial and an electrolyte which comprises at least one chemicalcolor-switching agent.

In accordance with yet another embodiment of the present invention thereis provided a non-electronic chemical sensing device comprising asurfactant-treated electrochromic metal diphthalocyanine complex and asuitable support material.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is anexploded view of the internal elements of a color-changingdisplay device in accordance with the invention;

FIG. 2 illustrates a cross-section through a portion of a color-changingdisplay device in accordance with the invention;

FIG. 3 is an exploded view of an optical filter in accordance with theinvention; and

FIGS. 4 and 5 are perspective views of chemical sensing devices inaccordance with the invention.

DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, there are shown the essential internal parts ofa chemically coupled color-changing matrix display device 10. A displaymatrix 12 comprises a plurality of coplanar, electronically isolateddots or elements of a solid, insoluble display material preferablydisposed in orthogonal rows and columns on a planar surface of aninsulating substrate 14. The display material is an insoluble dye whichis capable of reversibly changing color by reaction with solubleoxidizing and reducing agents that are electrochemically generated; itis described hereinafter. The substrate 14 may be of any compatiblematerial such as, for example, a plastic, glass or alumina plate or aplastic film. The substrate 14 is preferably of a material which hassubstantially the same thermal expansion coefficient as thecolor-changing material disposed thereon so as to promote good adhesionthereto. The better the adhesion, the longer will be the life of thedisplay device 10.

The remainder of the display device parts in FIG. 1 comprise drivematrix means for electrochemically generating the reactants, i.e.. thesoluble oxidizing and reducing agents. The reactants interact with thecolor-changing material to alter its color. The drive matrix is disposedparallel to and spaced apart from the planar surface of the substrate 14on which the display matrix 12 is disposed.

The drive matrix includes a first linear array or set of generatorelectrodes 16 and a second linear array or set of counter electrodes 18.Each electrode is a relatively long and narrow, isolated conductive unitdisposed parallel to the other electrodes of its array. The electrodesof each linear array are preferably disposed at right angles to ororthogonal to the electrodes of the other linear array in a distinctelectrode plane spaced apart from and parallel to the other electrodeplane. Both electrode planes are preferably parallel to the planarsurface of the substrate 14 on which the display matrix 12 is disposed.The generator electrode plane is closer to the display matrix 12inasmuch as it is interposed between the counter electrode plane and thedisplay matrix 12.

Each intersection of an individual generator electrode 16 and anindividual counter electrode 18 defines an electrode crossover region inwhich reactants for effecting color change are to be generated when anelectrical signal of appropriate magnitude and polarity is appliedacross a selected generator electrode-counter electrode combination.

In this embodiment, the substrate 14 acts as a spacer between thedisplay matrix 12 and the generator electrodes 16. The substrate andspacer 14 is porous enough to permit ready access of theelectrochemically generated reactants to the color-changing material.

The electrodes of one of the linear arrays are aligned with the rows ofdisplay elements in the display matrix 12 while the electrodes of theremaining linear array are aligned with the columns thereof. Therefore,each color-changing dot or element of the display matrix 12 is alignedwith a distinct generator electrode-counter electrode crossover region.This alignment is illustrated in FIG. 1 wherein the dashed line 20 isshown passing through the intersection or crossover region defined bythe third counter electrode 18 from the left edge and the thirdgenerator electrode 16 from the front edge in their respective electrodeplanes. The line 20 is shown extended to the display matrix 12 where itintersects the display element situated at coordinates X=3, Y=3 relativeto an origin at the intersection of the left and front edges of thedisplay matrix plane.

The display 10 is intended to be viewed in the direction indicated bythe arrow 22. This gives the more direct observation of the displaymatrix 12. If the display 10 is to be front-lighted, i.e., viewed byreflected light, the counter electrodes 18 can be opaque. However, for aback-lighted or projected display, the counter electrodes 18 must eitherbe transparent or semi-transparent. An open mesh structure will meet thelatter requirement. The generator electrodes 16 are also required tohave an open-mesh or similar structure so that reactants formed therecan escape and diffuse to the display matrix 12. For a back-lighted orprojected display, the generator electrodes 16 must be sufficientlytransparent for viewing by transmitted light.

Interposed between the generator electrodes 16 and the counterelectrodes 18 is a selective separator 24 which, in effect, divides theinterior of the display device into two compartments. The firstcompartment contains the generator electrodes 16 and the display matrix12 while the second compartment contains the counter electrodes 18. Theselective separator 24 prevents loss of electrochemically generatedreactant species from the compartment containing the generatorelectrodes 16 and the display matrix 12. Stated alternatively, theseparator 24 excludes or confines the electrochemically generatedreactant species away from the compartment containing the counterelectrodes 18. Thus, the generated reactants are preserved for reactionwith display material only. In addition, the separator 24 is required toconfine certain soluble chemical species to the compartment of thegenerator electrodes 16 and display matrix 12 and prevent contaminationof the counter electrodes 18 where these species could interfere withthe operation of the counter electrodes 18. Similarly, the separator 24is required to confine certain other soluble chemical species to thecompartment of the counter electrodes 18 and prevent contamination ofthe generator electrodes 16 and of the display material in the displaymatrix 12 where these other species could interfere with the operationof the generator electrodes 16 or with the operation of the displaymaterial. However, the separator 24 does permit the passage ofcurrent-carrying ions between the generator and counter electrode arrays16 and 18. A semi-permeable separator 24 made of, for example, an ionexchange resin is preferred but a retentive diffusion barrier containingelectrolyte may serve as an adequate separator 24 in some cases. An ionexchange resin exhibits selective permeability due to its ability totransport primarily cations or anions. A retentive diffusion barrierretards the undesired passage of chemical species because of itsmicroporous structure. The diffusion barrier can be of a microporouslayer of inert material fabricated by screening. Since these porouslayers are usually white, they can serve as optical backing in afront-lighted display or as a translucent light-transmitter in aback-lighted display. Alternatively, the separator 24 may be a molecularfilter having selective permeability due to its ability to transportonly chemical species smaller than a certain size. Excessive thicknessof the separator 24 will diminish pattern resolution in the drivematrix.

The generator electrodes 16 are preferably of a highly conductive, inertmaterial such as, for example, gold. The counter electrodes 18preferably include an electrochemical couple with insoluble activecomponents, such as silver-silver bromide, which will not impose specialrequirements on the separator 24. Soluble counter electrode couples suchas iodide-triiodide are not ruled out, however, if an appropriateseparator 24 is used. If both members of the counter-electrode coupleare soluble, as in the case of iodide-triiodide, the separator 24 mustbe retentive enough to exclude the more active member, such astriiodide, from the region of the display matrix 12.

The layer shown at 26 in FIG. 1 represents a body of electrolytesolution contacting the display matrix 12, the generator electrodes 16and the counter electrodes 18. The portion of the electrolyte solution26 in contact with the display matrix 12 and the generator electrodes 16initially contains a component of each of two redox couples. Asindicated above, any components of the redox couples that wouldinterfere with the operation of the counter electrodes 18 are excludedor confined away from the region of the counter electrodes 18 by theseparator 24. The initial component of one redox couple is in thereduced form while the initial component of the other redox couple is inthe oxidized form. The electrolyte solution 26 may also include an inertsupporting electrolyte. This may be a simple inorganic salt such as, forexample, potassium chloride. The initial redox couple components must becompatible with one another and with the color-changing material of thedisplay matrix 12 so that no color change or other change occurs untilan electrical signal is applied to the display.

When a current is passed in the drive matrix with the selected generatorelectrodes 16 as the anode and the selected counter electrodes 18 as thecathode, an oxidizing agent is formed at the surfaces of the generatorelectrodes 16. This reactant diffuses across the layer of electrolytesolution 26 from the generator electrodes 16 to the correspondinglyselected or addressed color-changing material in the display matrix 12.The oxidizing agent reacts with the color-changing material to changeits color and, in the process, is regenerated as the initial redoxcomponent in the reduced state. Thus, the soluble redox system mediates,or couples, the color-changing material in the display matrix 12 to thegenerator electrodes 16 without being consumed itself. In the displaycell 10, the anodic charge passed at the generator electrodes 16 shouldbe that required to completely convert the amount of color-changingmaterial present in the addressed elements of the display matrix 12. Oncontrolled electrolysis in the opposite direction, the component of theother redox couple generates a reducing agent which reacts with theoxidized color-changing material and brings it back to it initial colorstate. It is apparent that there is no net change in the color-changingmaterial or the reactants. Thus, the cycle should be repeatable manytimes. With some color-changing materials, if the reverse electrolysisis carried further by the passage of additional cathodic charge, thecolor-changing material may be reduced beyond its original color stateto a third or even a fourth color state. Hence, in addition to beingapplicable to two-color displays, the scheme of this invention isadaptable to the operation of multicolor displays wherein thecolor-changing material has more than two color states.

As will be apparent to those skilled in the art, the above-recitedprocess may be reversed in that the first reactant generated may be areducing agent such as, for example Fe(CN)₆ ³⁻ /Fe(CN)₆ ⁴⁻, to reactwith a suitable color-changing material to switch the material from itsinitial color state by reduction rather than by oxidation. It will alsobe apparent that further oxidized states may exist to provide additionalcolors.

By way of example, a suitable color-changing material for a displaydevice 10 in accord with the invention is lutetium diphthalocyanine,initially in a green color state. The initial soluble redox component inthe reduced form may be the bromide anion, Br⁻. When a current is passedin the drive matrix with the selected generator electrodes 16 as theanode and the selected counter electrodes 18 as the cathode, the bromideanion is oxidized at the generator electrodes 16 to form bromine, Br₂.The bromine reactant diffuses across the electrolyte layer 26 to thedisplay matrix 12 where the lutetium diphthalocyanine is switched fromits initial green color to an orange or a red color state by oxidation.In the process, the initial redox component the bromide anion Br⁻, isregenerated.

The cross-sectional view of the display device 10 in FIG. 2 is expandedto show certain of its details. A single generator electrode 16', havingan open mesh structure, extends horizontally and perpendicular to theplane of the drawing. A single counter electrode 18', also having anopen mesh structure, extends vertically and parallel to the plane of thedrawing. Interposed between the generator electrode 16' and the counterelectrode 18' is the selective separator 24.

A single, electronically isolated, distinct display element 12' ofcolor-changing material is shown disposed on the porous substrate andspacer 14 and aligned with the distinct intersection or crossover regionof generator electrode 16' and counter electrode 18'.

A front panel 28 for the display device envelope is of any suitabletransparent material such as a clear plastic or glass. A rear panel 30for the envelope may be of the same transparent material although it maybe of an opaque material if the display is to be front-lighted.

Two compartments 34 and 36 containing the body of electrolyte 26 areshown in FIG. 2. The compartment 34, shown to the left of the separator24, includes the generator electrode 16', the substrate and spacer 14and the display element 12'. The compartment 34 contains that portion ofthe body of electrolyte 26 having the redox components therein which areneeded to react at the generator electrode. The compartment 36, shown tothe right of the separator 24, includes the counter electrode 18'. Thecompartment 36 contains that portion of the body of electrolyte 26 fromwhich redox components are excluded unless some of them happen to becommon to the counter-electrode system. For example, a component such asbromide ion can be one of the main redox components, so that

    2Br.sup.- →Br.sub.2 +2e

at the generator electrode. Sometimes the same component can be part ofthe counter electrode system:

    AgBr+e→Ag+Br.sup.-.

In this case, one can use a separator 24 which is permeable to bromideion.

The compartments 34 and 36 are shown in FIG. 2 to have substantial sizefor the purpose of providing an excess of reactants. Longer device lifeis thereby provided in the event of gradual depletion of the reactantswhen the display device 10 is put in service. Where depletion is not afactor, the display device 10 can be made more compact by making thecompartments 34 and 36 smaller.

In the embodiment of FIGS. 1 and 2, the substrate and spacer 14supporting display element 12' controls the displacement between displayelement 12' and generator electrode 16'. The spacer 14 may betransparent, translucent or, when it is used as optical backing in afront-lighted display, white. It is necessary that the spacer 14 haverelatively high porosity. Electrolyte 26 fills the spacer pores whichmust be large enough to permit virtually unobstructed passage of thesoluble reactants.

The displacement or distance between the display element 12' and theportion of the generator electrode 16' in the crossover region ofgenerator and counter electrodes 16' and 18' is very small. This isnecessary for rapid switching of color, since a reactant must travel bydiffusion from its generation site across a layer of the electrolyte 26to display element 12'.

On the other hand, the distance from the intersection or crossoverregion of generator and counter electrodes 16' and 18' to the displayelements adjacent to display element 12' in display matrix 12 ispreferably sufficiently great that diffusion of reacants to theseadjacent display elements from the selected electrode crossover regionis insufficient to create a visible effect.

The electrolyte properties and the spacing between the generatorelectrodes 16 and the counter electrodes 18 in the drive matrix shouldbe chosen to give good resolution, i.e., to generate reactant only atthe selected intersections. This condition is approached by making thatportion of the drive matrix between the generator electrodes 16 and thecounter electrodes 18 relatively thin and of relatively highresistivity. Resolution is improved further if the separator 24 is amembrane having pores extending perpendicular to the membrade surface sothat the effective resistivity of the electrolyte-membrane layer isanisotropic. A threshold voltage in the electrochemical current-voltagecharacteristic at the generator or counter electrode surface is alsoconducive to good resolution.

It is preferable in the type of display described to address a selecteddisplay element with a current pulse, rather than a voltage pulse, sinceit is the amount of charge passed in generating a given amount ofreactant which is most closely related to the amount of color-changingmaterial to be switched. However, a voltage pulse of suitably controlledamplitude and duration may also be used.

Shown at 32 is a support for the multilayered central structure of thedisplay device 10 comprising the display matrix 12 and the drive matrix.The support 32 is preferably porous. It is also preferably transparentif the display device 10 is back-lighted. It may be discontinuous, vis,fabricated as a plurality of small spacer pads distributed over thestructure.

Although it is important to control the various thicknesses in themultilayer device structure according to the invention, this control isnot as difficult to achieve as in the fabrication of liquid crystaldisplay devices wherein relatively large rigid plates must be positionedclose together. The layer thicknesses in the present device can beachieved by screening or lamination techniques.

Referring now to FIG. 3, there are shown the essential parts of achemically coupled, color-changing optical filter 40. As shown, a cellhousing for the filter 40 includes an upper portion 44 and a lowerportion 58 enclosing a cell housing cavity. A filter element 42comprising a light-transmissive film of an insoluble color-changingmaterial is disposed on an interior surface of the upper cell housingportion 44. The filter element 42 may be of any insoluble color-changingmaterial which is capable of reversibly changing color by reaction withsoluble oxidizing and reducing agents that are electrochemicallygenerated.

The upper cell housing 44 may be of any material which is compatiblewith the color-changing material such as, for example, a plastic, glassor alumina.

The housing material and the color-changing material preferably havesubstantially the same thermal expansion coefficient so as to promotegood adhesion. The better the adhesion, the longer will be the life ofthe device 40.

In order for the device 40 to act as a light filter, both the upperportion 44 and the lower portion 58 of the cell housing must betransparent, at least in the viewing region.

The remainder of the device parts in FIG. 1 comprise the drive means forelectrochemically generating the reactants, i.e., the soluble oxidizingand reducing agents. The reactants interact with the color-changingmaterial to alter its color.

The drive means includes a generator electrode 46 of a transparentconductive material such as, for example, gold mesh. Generator electrode46 is disposed substantially parallel to, spaced apart from andcoextensive with the filter element 42.

Electrical contact with the generator electrode film 46 is preferablymade everywhere along the outer edge of the film through a peripheralstrip of metal and a conductor 54 extending external to the cell housingthrough a seal. Such geometry limits the ohmic resistance of theconductive film 46 to less than that of one square of the conductivematerial, even where the total area of the film 46 is large. Thislimitation on the electrical resistance of the generator electrodefavors uniform and rapid response over the entire area of the filterelement 42.

A counter electrode 48 is shown disposed on the interior side of theupper portion 58 of the cell housing. Since the central portion of thecell is shown occupied by the filter element 42, the counter electrode48 is shown disposed around the outer portion of the cell housingcavity. A conductor 56 provides an electrical path leading from thecounter electrode 48 external to the cell housing through a seal.

The cell housing cavity is filled with a body of electrolyte solution 50in contact with the generator electrode 46, the filter element 42 andthe counter electrode 48.

Interposed between the generator electrode 46 and the counter electrode48 is a selective separator 52 which, in effect, divides the cellhousing cavity into two compartments. The first or central compartmentcontains the counter electrode 48. The selective separator 52 preventsloss of electrochemically generated reactant species from the firstcompartment containing the generator electrode 46 and the filter element42. Stated alternatively, the separator 52 excludes or confines theelectrochemically generated reactant species away from the secondcompartment containing the counter electrode 48. Thus, the generatedreactants are preserved for reaction with color-changing material only.In addition, the separator 52 is required to confine certain solublechemical species to the compartment of the generator electrode 46 andfilter element 42 and prevent contamination of the counter electrode 48where these species could interfere with the operation of the counterelectrode 48. Similarly, the separator 52 is required to confine certainother soluble chemical species to the second compartment of the counterelectrode 48 and prevent contamination of the generator electrode 46 andof the color-changing material of the filter element 42 where theseother species could interfere with the operation of the generatorelectrode 46 or with the operation of the color-changing material.However, the separator 52 does permit the passage of current-carryingions between the generator and counter electrodes 46 and 48. Asemi-permeable separator 52 made of, for example, an ion exchange resinis preferred but a retentive diffusion barrier containing electrolytemay serve as an adequate separator 52 in come cases. An ion exchangeresin exhibits selective permeability due to its ability to transportprimarily cations or anions. A retentive diffusion barrier retards theundesired passage of chemical species because of its microporousstructure. The diffusion barrier can be a microporous structure of inertmaterial fabricated by screening. Alternatively, the separator 52 may bea molecular filter having selective permeability due to its ability totransport only chemical species smaller than a certain size.

As has been indicated, the generator electrode 46 is preferably of aconductive, inert material such as, for example, gold mesh. The counterelectrode 48 preferably includes an electrochemical couple withinsoluble active components, such as silver-silver bromide, which willnot impose special requirements on the separator 52. Soluble counterelectrode couples such as iodide-triiodide are not ruled out, however,if an appropriate separator 52 is used. If both members of thecounter-electrode couple are soluble, as in the case ofiodide-triiodide, the separator 52 must be retentive enough to excludethe more active member, such as triiodide, from the region of the filterelement 42.

The portion of the electrolyte solution 50 in contact with the filterelement 42 and the generator electrode 46 initially contains a componentof each of two redox couples. As indicated above, any components of theredox couples that would interfere with the operation of the counterelectrode 48 are excluded or confined away from the region of thecounter electrode 48 by the separator 52. The initial component of oneredox couple is in the reduced form while the initial component of theother redox couple is in the oxidized form. The electrolyte solution 50may also include an inert supporting electrolyte. This may be a simpleinorganic salt such as, for example, potassium chloride. The initialredox couple components must be compatible with one another and with thecolor-changing material of the filter element 42 so that no color changeor other change occurs until an electrical signal is applied to thedevice.

When a current is passed in the drive means with the generator electrode46 as the anode and the counter electrode 48 as the cathode, anoxidizing agent is formed at the surface of the generator electrode 46.This reactant diffuses across the layer of electrolyte solution 50 fromthe generator electrode 46 to the color-changing material in the filterelement 42. The oxidizing agent reacts with the color-changing materialto change its color and, in the process, is regenerated as the initialredox component in the reduced state. Thus, the soluble redox systemmediates, or couples, the color-changing material in the filter element42 to the generator electrode 46 without being consumed itself. In thedevice 40 the anodic charge passed at the generator electrode 46 shouldbe that required to completely convert the amount of color-changingmaterial present in the filter element 42. On controlled electrolysis inthe opposite direction, the component of the other redox couplegenerates a reducing agent which reacts with the oxidized color-changingmaterial and brings it back to its initial color state. It is apparentthat there is no net change in the color-changing material or thereactants. Thus, the cycle should be repeatable many times. With somecolor-changing materials, if the reverse electrolysis is carried furtherby the passage of additional cathodic charge, the color-changingmaterial may be reduced beyond its original color state to a third oreven a fourth color state. Hence, in addition to being applicable totwo-color displays, the scheme of this invention is adaptable to theoperation of multicolor displays wherein the color-changing material hasmore than two color states.

As will be apparent to those skilled in the art, the above-recitedprocess may be reversed in that the first reactant generated may be areducing agent to react with a suitable color-changing material toswitch the material from its initial state by reduction rather than byoxidation. It will also be apparent that further oxidized states mayexist to provide additional colors.

By way of example, a suitable color-changing material for a device 40 inaccordance with the invention is lutetium diphthalocyanine, initially ina green color state. The initial soluble redox component in the reducedform may be the bromide anion, Br⁻. When a current is passed in thedrive means with the generator electrode 46 as the anode and the counterelectrode 48 as the cathode, the bromide anion is oxidized at thegenerator electrode 46 to form bromine, Br₂. The bromine reactantdiffuses across the electrolyte 50 to the filter element 42 where thelutetium diphthalocyanine is switched from its initial green color to ared color state by oxidation. In the process, the initial redoxcomponent, the bromide anion Br⁻, is regenerated.

Referring now to FIG. 4, there is shown a non-electronic chemicalsensing device for indicating the presence of at least a minimal levelof a hazardous gas such as chlorine. The device 60 comprises abadge-like frame 62 having means 64 for attaching device 60 to a garmentor other surface, and an exposed film 66 of surfactant-treated colorchanging display material. Alternatively, as shown in FIG. 5, a film 68of color changing material may be disposed as a suitable flexiblesupport to having an adhesive 72 on the reverse side thereof, forapplication to a surface. Upon exposure to gaseous chlorine, forexample, the surfactant-treated material undergoes a color change.

The electrochromic metal diphthalocyanine is a complex moleculecomprising two phthalocyanine ring structures which are generallybelieved to lie in substantially parallel planes with a metaliondisposed between the planes occupied by the phthalocyanine rings. In apreferred embodiment, the metal in the complex is yttrium, scandium or arare earth of the lanthanide series; however, other metals whosediphthalocyanine complexes are electrochromic may be used. In apresently preferred embodiment, the metal diphthalocyanine complex islutetium diphthalocyanine.

The metal diphthalocyanine complexes for utilization in this inventionmay be synthesized by methods which have been described in theliterature. It is preferred to purify the metal-diphthalocyaninecomplexes by vacuum sublimation in order to obtain high purity films ofthe diphthalocyanine complexes in display cells. The diphthalocyaninefilm is preferably deposited by vacuum sublimation of a diphthalocyanineat pressures on the order of 10⁻⁶ mm to 10⁻⁵ mm of Hg. Duringsublimation of the diphthalocyanine the source of the diphthalocyanineis held at a temperature which provides a reasonable deposition ratewithout destroying the complex. This temperature may be in the range ofabout 300° C. to 400° C.

The color changing material film thickness should be in the range ofabout 0.05 to 1.0 micron, preferably about 0.1 to 0.2 microns dependingon the intensity of color desired.

The color changing material is treated, prior to use, with at least onesurface-active agent carried in a suitable liquid vehicle, as disclosedin the aforementioned application Ser. No. 330,041, filed Dec. 11, 1981.A suitable mixture for treating the electrochromic display materialconsists essentially of about one to one-and-one-half grams per liter ofboth substituted imidazoline and silicone glycol in approximately equalproportions in acetone. The acetone mixes sufficiently well with thesurfactants so that a satisfactory deposit of surfactants is formed whenthe acetone is removed. A satisfactory deposit is one that is uniformand free of spotting. Acetone has an advantage in that it is highlyvolatile and may be readily driven off by air drying. Other, lessvolatile liquid vehicles may be removed by careful heating and/orevaporation under vacuum.

The electrolytes 26 and 52 consist essentially of at least one colorswitching agent and a fluid carrier. The color switching agent is anoxidizing agent such as, for example, potassium ferricyanide, cericnitrate, ceric sulfate, potassium dichromate, bromine, chlorine, and thelike. The fluid carrier is an aqueous electrolyte such as, for example,1N H₂ SO₄, 1N HClO₄, 1N HCl, 1N KCl and the like, or, in the case ofbromine and chlorine, the gas itself. The concentration of the colorswitching agent in the fluid carrier can range from about 0.001N toabout 0.1N, preferably about 0.01N.

The following example illustrates the invention:

EXAMPLE

The responses of green lutetium diphthalocyanine films on tin oxide tovarious electrolyte-redox systems are given in the following table. Thefilms were treated using a dilute solution of Dow-Corning 193 (siliconeglycol) and Witcamine AL 42-12 (imidazoline/tall oil derivative).

                  TABLE                                                           ______________________________________                                        Electrolyte-Redox System                                                                E°              Reaction Time                                Couple    V vs. SHE  Observed Color                                                                            (sec)                                        ______________________________________                                        Fe.sup.3+ /Fe.sup.2+                                                                    0.68       Olive       240                                          1N H.sub.2 SO.sub.4                                                           Fe.sup.3+ /Fe.sup.2+                                                                    0.75       Orange      240                                          1N HClO.sub.4                                                                 Fe.sup.3+ /Fe.sup.2+                                                                    0.77       Orange      120                                          1N HCl                                                                        Br.sub.2 /Br.sup.-                                                                      1.09       Orange       15                                          (Gaseous)                                                                     Cr.sub.2 O.sub.7.sup.2- /Cr.sup.3+                                                      1.35        Orange,    120                                          dilute H.sub.2 SO.sub.4                                                                            Slight Olive                                             Cl.sub.2 /Cl.sup.-                                                                      1.36       Orange       5                                           (Gaseous)                                                                     Ce.sup.4+ /Ce.sup.3+                                                                    1.44       Orange       5                                           dilute H.sub.2 SO.sub.4                                                       ______________________________________                                    

While the invention has been described with respect to preferredembodiments thereof, it will be appreciated by those skilled in the artthat various changes in form and detail may be made therein withoutdeparting from the spirit and scope of the invention.

We claim:
 1. In a device comprisinga matrix having a plurality ofdistinct electronically isolated elements of a solid insoluble displaymaterial capable of changing color by reaction with soluble reactants;and drive means for electronically generating said soluble reactants ata distinct region in said drive means, wherein one distinct region insaid drive means is associated with one of said distinct elements of thedisplay material; wherein a selected one of said distinct elements ofdisplay material receives said soluble reactants by diffusion from saidone distinct region in said drive means associated therewith, theimprovement wherein said display material is a surfactant-treated colorchanging metal-diphthalocyanine complex.
 2. The device of claim 1wherein said complex is a lutetium diphthalocyanine complex.
 3. Thedevice of claim 1 wherein said soluble reactants are selected from thegroup consisting of Fe³⁺ /Fe²⁺, Ce⁴⁺ /Ce³⁺, Cr₂ O₇ ²⁻ /Cr³⁺, Br₂ /Br⁻and Cl₂ /Cl⁻.
 4. The device of claim 3 wherein at least one of saidsoluble reactants is carried in aqueous fluid carrier solution.
 5. Thedevice of claim 4 wherein said fluid carrier is an aqueous acidsolution.
 6. The device of claim 1 wherein said display material is ametal diphthalocyanine complex treated with a mixture of silicone glycoland imidazoline surfactants.
 7. A chemical sensing device comprising afilm of surfactant-treated color changing metal-diphthalocyanine complexand means for supporting said film.
 8. The device of claim 7 whereinsaid supporting means is a frame including means for attaching saidsupporting means to a surface.
 9. The device of claim 7 wherein saidsupporting means is a flexible support having an adhesive backing. 10.The device of claim 7 wherein said complex is lutetium diphthalocyanine.